The invention relates to floor-leveling mechanism for a cable-suspension elevator system, wherein an elevator cage and its counterweighting are cable-connected and suspended over a drive sheave at the top of an elevator shaft.
In a typical elevator system of the character indicated, say for a fully automatic 2000-lb. capacity elevator having a traveling speed of 100 feet per minute, the hoist engine for driving the drive sheave may consist of 7.5-horsepower electric motor, a worm reduction-gear unit, and an elevator-brake assembly wherein brake action is mechanically applied and power-released. Vertical rails guide the elevator cage, and plural counterweights are suspended by four steel traction cables, one end of each cable being secured to the crosshead of the cage, and the opposite ends being secured to the counterweights. These four cables pass over the traction sheave of the hoist engine and rest in traction grooves. Control may be of an automatic selective collective pushbutton type, and floor-leveling involves drive-motor and/or brake actuation at the hoist engine, as dictated by level-detection at the particular selected landing level.
A variety of leveling-control systems exists, with various degrees of sophistication in regard to precision of landing-level detection and motor/brake action in response to such detection. However, such approaches to the problem necessarily involve varying degrees of cable-stretch effects, depending upon instantaneous cage load and upon the instantaneous length of the cable suspension, from sheave to cage. Necessarily also, any given automatic positioning involves multiple and varied operations of the drive motor and/or brake mechanism, which operations are of vastly different nature from the primary raising and lowering functions of the hoist engine. Moreover, the precision requirements of floor-leveling to meet specifications for the safety of handicapped persons impose severe demands on the complexity and sophistication of the hoist engine and its control.